1. Field of the Invention
The present invention relates to a silver halide photographic light-sensitive material which forms direct positive photographic images, more particularly, to a photographic light-sensitive material having a photographic emulsion layer or a hydrophilic colloid layer containing a novel compound as a fogging agent.
2. Description of the Prior Art
In the field of silver halide photographic methods, a photographic method where photographic images can be obtained without forming negative images or without carrying out any intermediate processings for forming negative images is called a direct positive photographic method, and the photographic light-sensitive materials and the photographic emulsions that are employed in such a photographic method are called direct positive light-sensitive materials and direct positive photographic emulsions, respectively.
There are various types of direct positive photographic methods. Among these methods, a more useful method is one which comprises exposing fogged silver halide grains in the presence of a desensitizer and then developing the same, or one which comprises exposing a silver halide emulsion predominantly containing silver halide grains having light-sensitive nuclei inside the grains and then developing the same in the presence of a fogging agent. This invention belongs to the latter method.
A silver halide emulsion containing silver halide grains predominantly having light-sensitive nuclei inside the grains which are capable of forming latent images inside grains is called an internal latent image type silver halide emulsion.
Methods for obtaining direct positive images by the surface development of an internal latent image type silver halide photographic emulsion in the presence of a fogging agent, and a photographic emulsion or light-sensitive material employed in such methods are disclosed in U.S. Pat. Nos. 2,456,953, 2,497,875, 2,497,876, 2,588,982, 2,592,250, 2,675,318 and 2,675,318, British Pat. Nos. 1,011,062 and 1,151,363, and in Japanese patent publication No. 29,405/68.
In the above-mentioned methods for obtaining direct positive images, a fogging agent can be added to a developing solution, but more preferably is added to a photographic emulsion layer or another layer of a light-sensitive material to adsorb it to the surface of the silver halide grains because better reversal photographic properites are obtained.
As the fogging agents which are added to a silver halide emulsion layer or another layer of a light-sensitive material, hydrazine compounds are known as disclosed in U.S. Pat. Nos. 2,563,785 and 2,588,982. However, where hydrazine compounds are added to a silver halide emulsion layer, a high concentration thereof (e.g. about 2 g per 1 mol of silver) is necessary, and the concentration thereof in the emulsion layer changes because they are dissolved out from the emulsion layer into a developing solution in development, whereby maximum density (unexposed areas) becomes irregular, and, in a multilayer light-sensitive color photographic material, the fogging effects between the emulsion layers become unbalanced.
In order to avoid these defects, it was proposed in U.S. Pat. Nos. 3,615,615, 3,719,494, 3,734,738 and 3,759,901 that a heterocyclic quaternary salt compound be used as a fogging agent. However, there are many cases where a spectral sensitizing dye is added to the silver halide emulsion for spectral sensitization. Particularly, color light-sensitive materials must have layers sensitive to green light and red light together with a blue-sensitive layer, and so the green-sensitive and red-sensitive emulsion layers always contain spectral sensitizing dyes.
Where fogging agents are present together with spectral sensitizing dyes for green light and red light in the direct positive emulsion, competitive adsorption to the silver halide emulsion takes place between the spectral sensitizing dyes and the quaternary salt fogging agent. Therefore, if the fogging agents are added in an amount necessary to form the desired nuclei, the spectral sensitization effects are prevented, and if the spectral sensitizing dyes, on the other hand, are added in the concentration necessary to obtain the desired spectral sensitization, the formation of fogging nuclei is prevented as well.
In order to overcome this difficult problem, it is known from U.S. Pat. No. 3,718,470 that spectral sensitizing dyes having nucleating substituent groups in the dye molecules can be employed.
However, according to the method in which both a fogging function and a spectral sensitizing function are provided to one molecule, there are defects that if the material is used in an amount necessary for spectral sensitization, a sufficient fogging effect cannot be obtained, while if the material is used in an amount necessary for fogging, insufficient spectral sensitization is obtained.
To overcome the above defect, there are needed fogging agents which can easily be adsorbed onto silver halide grains and form desired nuclei in such an amount as not to prevent a spectral sensitizing effect.